The invention relates generally to digital data processing and, particularly, to reconstructive imaging. The invention has application in heath care and, specifically, medical imaging—as well as in a host of other areas, such as industry, research and defense.
Reconstructive imaging—that is, the construction of a three-dimensional representation (image) of a volume from two-dimensional measured projection images of that volume, e.g., obtained by an x-ray imaging apparatus—is highly computation intensive. For example, computed axial tomography (CAT) is an imaging technique in which three-dimensional views of the internal structures of an object—typically, a head or other portion of the human body—are constructed from a series of x-ray projections (or scans) taken at a plurality of angles around the object.
With the aid of a computer, those scans can be computationally transformed (e.g., using techniques such as back-projection) to discern the internal structures of the object (e.g., in the case of a head, the skull, gray matter and other imageable structures). While none of those transformations is, in itself, sufficient to identify those structures, the computational combination of all of the transformations typically is. Because this requires processing hundreds, if not thousands, of projected images, it typically requires special-purpose hardware in order to provide real-time results. Though prior art solutions have proven effective in this regard, they are typically quite expensive.
Moreover, many prior solutions—particularly, for example, those, for determining back-projections have limited applicability to a new class of imaging, referred to as tomosynthesis, in which a relatively small number of projection images are required from only a limited number of x-ray source positions (or foci). In these systems, the computational transformations include not only back-projections, but also forward-projections, in which estimates of the volume being reconstructed are projected “forward” to generate hypothetical (synthetic) projection images for computational comparison with actual measured projection images acquired by the imaging equipment. By comparing the hypothetical forward projection of the current 3D model to the measured projection images, a correction image can be calculated and used to update (modify) the current 3D model.
CAT scanners and tomosynthesis systems are not the only medical imaging equipment that use forward-projections and/or back-projections. Forward-projection and back-projection operations also form the basis of a broader class of computer-based imaging techniques, referred to as computed tomography (CT), as well as positron emission tomography (PET), single photon emission computed tomography (SPECT), to name but a few. In addition, forward-projection and back-projection are used outside the medical field, for example, in manufacturing (e.g., to inspect articles for defects), securing (such as baggage scanning) in research, defense and so forth.
An object of the invention is to provide improved digital data processing apparatus and methods. Another object is to provide such apparatus and method as can be applied to reconstructing images, e.g., of the type discussed above (by way of non-limiting example).
Other objects of the invention are to provide such apparatus and methods that can perform reconstructive imaging more efficiently. Another object of the invention is to provide such methods and apparatus that can be implemented with less expensive equipment, off-the-shelf or otherwise.